In conventional color electrophotography, a series of electrostatic images are created on an image member. They are toned with different color toners and then transferred in registration to a receiving surface to create a multicolor toner image. Typically, the receiving surface is a receiving sheet of paper of similar material which is then secured around the periphery of a transfer drum. The transfer drum is rotated in contact or near contact with an image member to repeatedly bring the receiving sheet into transfer relation with the consecutive images to overlay them in registration.
It is also known to transfer a series of color toner images in registration directly to the periphery of the transfer drum to create the multicolor image on the surface from which it is transferred in a single step to a receiving sheet.
As color toners get finer, for example, less than 10 microns, especially less than 3.5 microns, higher resolution becomes possible, even approaching that of conventional silver halide photography.
Such apparatus operates to sequentially scan each of the image frames on the original filmstrip (e.g., a 35 mm color negative filmstrip) and produce, by an electrophotographic printing process, full-color prints on a non-photosensitive photosensitive print-receiver sheet, such as a sheet of paper having a thermoplastic coating. The electrophotographic process involves the steps of forming a set of different color-separated toner images (e.g., cyan, magenta and yellow toner images) on a reusable photoconductive recording element, one set for each original image frame, and transferring such images in registration to the print receiver sheet.
To facilitate sheet handling in the above apparatus, as well as to enhance the efficiency of the overall print-making process, each print receiver sheet is considerably larger in size than the commonly desired sizes of photographic prints. Thus, it is disclosed that several color prints be formed on each receiver sheet. For example, assuming the receiver sheet having a size (in inches) of 12.times.18, it is disclosed that nine 4.times.6 prints be produced on the receiver sheet in a 3-by-3, 2-dimensional array. This 3-by-3 array, sometimes referred to as "9-up" format, would be a desirable format due to the current popularity of photographic prints of the 4.times.6 inch size. In the event larger prints (e.g., 5.times.7 inch) are desired, four of such prints may be formed on a receiver sheet of this size, in a 2-by-2, or "4-up", format. Upon forming multiple images on a receiver sheet, the receiver sheet is cut to revive the smaller format prints or "snapshots".
To produce full color prints by any of the various non-photographic techniques, e.g., by electrophotographic, thermal/dye-sublimation and ink jet technology, it is necessary to sequentially record a series of color-separated images, viz. cyan, magenta and yellow images, on an image-recording member. These images are either directly recorded, in registration, on the ultimate print-receiving medium, as is the case for thermal and ink-jet recording, or, as indicated above in the case of electrophotographic recording systems, recorded on a reusable recording element from which the images can be transferred, in registration, to the print-receiving medium. In either case, information required to produce these color-separated images can be provided by scanning a color negative filmstrip, one frame at a time and pixel-by-pixel, with an electronic scanning device, e.g., a color-responsive charge-coupled device (CCD). Such scanning devices provide a set of color-separated signals, each of such signals representing the spectral content of the photographically recorded image at three different wavelength regions, e.g., the red (R), green (G), and blue (B) spectral regions. Alternatively, the color-separated R, G and B signals can be computer-generated or read off from a ROM (e.g., a compact disc).
In conventional photographic photo finishing, the print medium takes the form of a strip of photosensitive paper, and multicolor images are printed directly thereon in the same order as they appear on the filmstrip. A strip format is performed through the photographic print medium since it is much easier to advance an elongated strip through the chemical baths required to develop the latent images formed thereon than it is to advance sheet material through the processing baths. Moreover, since multiple color-separated images can be printed simultaneously and in registration on a photographic emulsion, it is possible to use the output of a film scanner directly to control the exposure source of the printer with little or no need to buffer or store the scanner output.
But in the case of non-photographic photofinishing, where multiple full-color images are to be formed on a single sheet of printing material, there is a need to store relatively vast quantities of colored image information before the printing of the first, multiframe, color-separated image frame can begin. For example, before the first color-separated image of a "9-up" format can be formed on the photoconductive recording element of the electrophotographic printer mentioned above, it is necessary to store 27 color-separated images (i.e., 9 images times 3 color separations each).
Electronic printing, such as electrophotographic reproduction, by an apparatus performing photofinishing of images contained in an original filmstrip or the like (e.g., a 35 mm color negative filmstrip) has been shown and described in U.S. Pat. No. 5,040,026, issued Aug. 13, 1991 in the name of Jamzadeh et al. Such apparatus operates to sequentially scan the respective image frames of an original filmstrip and produce, by an electrophotographic process, full color prints on a non-photosensitive print receiver sheet. In the electrophotographic process, a set of color separation marking particle images (e.g., cyan, magenta, and yellow) are formed on a reusable photoconductive recording member, one set for each of the respective original image frames on the filmstrip. The set of color separations marking particle images are transferred and registered to a print receiver sheet to form the desired full color print.
It has been found that when multiple prints are produced on a receiver sheet in the above-described manner, there are certain conditions imposed on the electronic printing process which may have an adverse effect on the quality and quantity of the completed prints. With the electronic color printing of images, it is desirable to have the process functions thereof optimized, based on information data, of images to be printed, there may be obtained during a low resolution pre-scan of said images. Prints are produced by pre-scanning, at low resolution, an array of images contained on respective frames of a filmstrip or the like. Information data, obtained during low resolution pre-scanning of at least the scene content of the respective images, are stored and operating parameters based on the stored information data are calculated to determine required process functions for the electronic printing process. Based on the determined required process functions, for the electronic printing process are set in a manner to optimize the process.
U.S. Pat. No. 4,705,386 describes a color copying machine that includes a scanning device for applying illumination onto a color original to effect a scanning operation. Because the yellow, magenta and cyan tones are sequentially transferred onto the single record sheet to achieve a color copy, each toner image must be transferred accurately to the same position on the second sheet for a good quality copy. This requires that the drive mechanism for the scan system, the photoconductive drum and the transfer drum must be operated in synchronism with one another. The photoconductive drum and the transfer drum are connected together through a gearing with little backlash so that they are rotated together with each other. The drive mechanism for the scan system comprises a servomotor which has a high responsiveness in speed control. With such drive systems, the peripheral length L of the transfer drum determines that one set of scanning and retrace (i.e., scanning back) with respect to a second sheet is for the maximum size, A3-size which is effected per one revolution of the transfer drum.
Accordingly, it can be seen that the invention improves copier productivity only when dealing with sheets smaller than the maximum size. The scanner retrace time is designed to match the non-image area of the drum (PC or transfer) when the maximum size sheet is used. Thus, it can be seen that for smaller sheets, this non-image gap increases and to impair productivity by retracing the scanner and begin exposing onto the PC-drum regardless of where it is; this is workable when a seamless drum is used. The extra gap on the transfer drum is compensated by speeding that drum.
It should be noted that unless the scanner as well as the drums are both sped up, the scanner retrace time matches the rotation of the non-image area of the drum for the small sheet. This requires that when dealing with the large sheets of paper, the scanner must retrace faster because the non-image gap area will be less (shorter). Such a productivity gain would require variable speed control on the scanner motor.